Compositions and membranes comprising thermoplastic olefin (TPO) polymers have found widespread use in the roofing industry for commercial buildings. TPO membranes are often fabricated as a composite structure containing a reflective membrane (40 to 60 mils thick), a reinforcing polyester scrim fabric (1 to 2 mils thick), and a pigmented layer (40 to 60 mils thick). When the membrane is applied to the roof, the reflective white layer is exposed to sunlight while the pigmented layer (which is underneath the reflective layer) is attached to the roof insulation material.
For roofing and other sheeting applications, the products are typically manufactured as membrane sheets having a typical width of 10 feet (3 meters) or greater, although smaller widths may be available. The sheets are typically sold, transported, and stored in rolls. For roofing membrane applications, several sheets are unrolled at the installation site, placed adjacent to each other with an overlapping edge to cover the roof and are sealed together by a heat welding process during installation. During transport and storage, the rolls can be exposed to extreme heat conditions, such as from 40° C. to 100° C., which can lead to roll blocking of the rolls during storage in ware-house. After installation, the membranes can be exposed during service to a wide range of conditions that may deteriorate or destroy the integrity of the membrane. As such, a membrane is desired that can withstand a wide variety of service temperatures, such as from −40° C. to 40° C.
PCT Publication No. WO 2010/115079A1 is directed to roofing membranes that contain compositions of Formula I that comprises (a) 30 to 50 wt % of a propylene-based elastomer, (b) 9 to 20 wt % of a plastomer, (c) from 7 to 20 wt % of an impact polypropylene-ethylene copolymer, (d) 20 to 35 wt % of magnesium hydroxide, (e) 5 to 10 wt % of titanium dioxide, and (f) 1 to 2 wt % of additives; or compositions of Formula II that comprises (a) 32 to 48 wt % of a propylene-based elastomer, (b) 9 to 18 wt % of a plastomer, (c) 7 to 20 wt % of an impact polypropylene-ethylene copolymer, (d) 25 to 35 wt % of magnesium hydroxide, (e) 4 to 6 wt % of titanium dioxide, (f) 0.75 to 1.5 wt % of UV inhibitor, (g) 0.2 to 0.45 wt % of antioxidant/stabilizer, (h) 0.15 to 0.4 wt % of thermal stabilizer, and (i) 0.1 to 0.2 wt % of lubricant. The propylene-based elastomer used in WO 2010/115079A1 was Vistamaxx™ 6102 and the lubricant used was Asahi AX71 which is a mono or di-stearyl acid phosphate. The roofing membrane in WO 2010/115079A1 is formed around a scrim having reinforcing polyester threads.
PCT Publication No. WO 2014/001224A1 is directed to compositions comprising 40 to 75 wt % of at least one polypropylene-based elastomer and around 25 to 60 wt % of at least one random copolymer of polypropylene. The polypropylene-based elastomers used in WO 2014/001224A1 were Vistamaxx™ 3980, 6102, and 6202.
PCT Publication No. WO 2014/040914A1 is directed to thermoplastic mixtures that comprise at least one impact-resistant polypropylene copolymer and at least one ethylene-1-octene copolymer, where the weight ratio of impact-resistant polypropylene copolymer to ethylene-1-octene copolymer is in the range of 35:65 to 65:35.
U.S. Patent Ser. No. 62/121,230, filed on Feb. 26, 2015, is directed to a roofing membrane composition of a 10-50 wt % of a propylene-based elastomer, 5-40 wt % of a thermoplastic resin, at least one flame retardant, and at least one ultraviolet stabilizer.
There still remains a need for roofing membranes that demonstrate flexibility at service temperatures from −40° C. to 40° C. and resistance to roll blocking at elevated temperatures.